"Mitt Romney is a stiff. Mitt Romney will not get elected. Mitt Romney failed twice and really failed last time," Trump said on NBC's "Today" show, referring to Romney's two past presidential bids.

Romney is set to address the 2016 race later in the day at the University of Utah.

According to excerpts of Romney's speech leaked Thursday morning, the GOP's 2012 presidential nominee will declare Trump as utterly unelectable compared to his primary rivals.

"Donald Trump is a phony, a fraud. His promises are as worthless as a degree from Trump University. He's playing the American public for suckers," Romney will reportedly say.

"His domestic policies would lead to recession. His foreign policies would make America and the world less safe. He has neither the temperament nor the judgment to be president," he'll add.

In his whirlwind of Thursday-morning interviews and tweets attacking Romney, Trump reminded the public that Romney sought his endorsement four years ago.

"He begged me four years ago for my endorsement — I mean, literally begged me," Trump said on the "Today" show. "And he's a failed candidate. I mean, frankly, I backed him; he failed. He was a horrible candidate, didn't know what he was doing."